Currently, with the enhancement of people's awareness of protecting the environment and saving energy, a new generation of semiconductor lighting sources has become the mainstream lighting source due to its high efficiency, low consumption, energy conservation, environment protection, rapid response, long service life and the like. Nowadays, many common lighting products make use of the silicon controlled dimming solution, which seeks to ensure the normal operation of a dimmer system with minimal cost and without changing the dimmer system, and provides the power source with a high-precision constant current function and a high power factor.
For existing control chips which realize the high-precision constant current function and the high power factor, many elements must be connected to the peripheral system to ensure normal operation of the silicon controlled dimmer as shown in a dashed box of FIG. 1. In conventional solutions, a fourteenth resistor R14 is used as a dummy load to provide a conduction circuit for the silicon controlled rectifier to ensure normal timing of the silicon controlled dimmer. However, when the silicon controlled rectifier is conducted, the conduction current in the silicon controlled rectifier is great, even reaches to dozens of milliamperes, which may result in that the fourteenth resistor R14 consumes too much power. Thus, the tenth resistor R10, the twelfth resistor R12, the fifteenth resistor R15, the third triode Q3, the thirteenth resistor R13 and the seventh capacitor C7 start timing after the silicon controlled rectifier is conducted, and control the second MOS transistor Q2 to turn on to short the fourteenth resistor R14, thus reducing the power consumption of the fourteenth resistor R14. The third triode Q3 is configured to leak electric charges in the seventh capacitor C7 to ensure that the tenth resistor R10, the twelfth resistor R12, the fifteenth resistor R15, the third triode Q3, the thirteenth resistor R13 and the seventh capacitor C7 start to time normally after the silicon controlled rectifier is conducted such that the second MOS transistor Q2 is controlled to turn on when the next timing starts. Apparently, to ensure normal operation of the silicon controlled dimmer, the conventional solution requires many elements, which increases the cost of the power source.